1. Field of the Invention
This invention relates to the robotic control of position tracking, alignment, and assembly of large-scale industrial equipment, and more particularly, to a large scale metrology system.
2. Description of Related Art
Large-scale metrology systems used for the factory assembly of industrial equipment are known. These metrology systems typically include both target-sensors and laser-transmitters. During operation in an aircraft assembly facility for example, a number of the target-sensors are placed on the major components of an airplane to be assembled, such as the fuselage, wings, tail, etc. The laser-transmitters are positioned at various locations across the assembly floor. The laser-transmitters, which each rotate at a different rate, each generate a fan-beam pair. In addition, each of the laser-transmitters also generates an optical “flash” beam every two rotations. The flash beam is generated when the laser-transmitter is at a “zero” degree reference position.
As each of the laser-transmitting heads rotate, the corresponding fan-beam pairs sweep across the target-sensors. In response to each fan-beam pair, each target-sensor generates a pulsed pair of signals, which are provided to a central computer. For each of the pulsed pair of signals, the central computer determines:
(i) the corresponding laser-transmitting head, among the plurality of heads, resulting in the pulsed pair of signals. Since each head rotates at a different rate, the time for each fan-beam pair to make a full rotation is different. Based on this timing information, the corresponding laser-transmitting head that resulted in the generation of the pulsed pair of signals can be determined;
(ii) the azimuth of the target relative to the zero reference position of the corresponding head. The azimuth is determined by the rotational angle of the fan-beams when detected by the target relative to the zero degree reference position, as defined by the flash beam; and
(iii) the elevation of the target-sensor relative to the corresponding head based on the timing between the first pulse and the second pulse of the pulsed pair of signals.
The central computer then generates a vector for each pulsed pair of signals. Each vector originates at the identified corresponding head and is defined by the determined azimuth and elevation. The central computer then determines the location of the targets where two or more of the vectors intersect.
The above-described process is continuously performed during the assembly operation. As the components to be assembled are moved, the location of the targets is tracked in real-time. The robot system in response makes adjustments on the fly, resulting in more accuracy and precision during assembly.
Although advantageous, the above-described metrology system has a number of issues that are less than ideal. With the optical flash beam, it is difficult to generate a well-defined signal on the order of nanoseconds. As a result, the timing of the signals received from the laser-transmitting heads with respect to the zero reference position of a head may be inaccurate. In addition, the flash beams will often reflect off of non-target surfaces, such as windows in the assembly area or even the objects to be assembled, particularly if they are made of highly reflective surfaces, such as metal. As a result, stray pulses may be generated, causing false or inaccurate azimuth calculations to be performed. Both of these factors reduced the accuracy of the current metrology systems.